sctp: sysctl: auth_enable: avoid using current->nsproxy

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: sctp: sysctl: auth_enable: avoid using current->nsproxy As mentioned in a previous commit of this series, using the 'net' structure via 'current' is not recommended for different reasons: - Inconsistency: getting info from the reader's/writer's netns vs only from the opener's netns. - current->nsproxy can be NULL in some cases, resulting in an 'Oops' (null-ptr-deref), e.g. when the current task is exiting, as spotted by syzbot [1] using acct(2). The 'net' structure can be obtained from the table->data using container_of(). Note that table->data could also be used directly, but that would increase the size of this fix, while 'sctp.ctl_sock' still needs to be retrieved from 'net' structure.

References

• https://git.kernel.org/stable/c/cf387cdebfaebae228dfba162f94c567a67610c3
• https://git.kernel.org/stable/c/dc583e7e5f8515ca489c0df28e4362a70eade382
• https://git.kernel.org/stable/c/bd2a2939423566c654545fa3e96a656662a0af9e
• https://git.kernel.org/stable/c/1b67030d39f2b00f94ac1f0af11ba6657589e4d3
• https://git.kernel.org/stable/c/7ec30c54f339c640aa7e49d7e9f7bbed6bd42bf6
• https://git.kernel.org/stable/c/c184bc621e3cef03ac9ba81a50dda2dae6a21d36
• https://git.kernel.org/stable/c/15649fd5415eda664ef35780c2013adeb5d9c695